Paint binders are disclosed in DE-OS No. 23 20 301, corresponding to Canadian Pat. No. 1,021,493, which are obtained by reaction of MANNICH-bases (of condensed phenols, secondary alkanolamines and formaldehyde) with an epoxy resin. Similar binders are disclosed in DE-OS No. 24 19 179, corresponding to U.S. Pat. No. 3,994,989. As stated in DE-OS No. 27 11 385, such systems have the disadvantage that amines are split-off on stoving. Therefore, it has been proposed to use a MANNICH-condensation product of a phenol and/or an alkylphenol, a primary amine, and formaldehyde.
Another proposal for improving the products of the DE-OS No. 23 20 301 and DE-OS No. 24 19 179 references is disclosed in DE-OS No. 27 11 425, corresponding to U.S. Pat. No. 4,134,932, where to such binders water-insoluble urethane group carrying resins are added, and in particular the modified polyamide amine resins. To avoid the splitting off of amines, DE-OS No. 25 41 801, corresponding to U.S. Pat. No. 4,086,292, proposes to react the MANNICH-base with an epoxy resin based on polyhydric alcohols, the hydroxy groups of which are reacted with semi-blocked diisocyanates and optionally with a urethane-free epoxy resin. DE-OS No. 25 54 080, corresponding to Canadian Pat. No. 1,074,489, describes a similar process. In all these cases the reaction with the isocyanates is to suppress the split-off of amines on stoving.
The products produced according to the teachings of the aforesaid references, however, do not meet the requirements of the automobile industry with respect to corrosion resistance at crosslinking temperatures of from about 150.degree. to 170.degree. C. and the adhesion of the stoved film, particularly the adhesion of subsequent coats.